Variable flux-reset ferroresonant voltage regulator

ABSTRACT

A thyristor controlled ferroresonant voltage regulator circuit in which the output voltage is made adjustable by varying the reset flux level of each of two parallel magnetic core paths upon which the load windings are wound. One magnetic core path is driven hard into magnetic saturation during one half cycle of the output waveform, and the second magnetic core path is clamped at a given value; in the second half cycle the second path is driven into magnetic saturation and the one path is clamped at the given value. The level of clamping is determined by an associated control circuit which may comprise a simple manually adjustable potential source, or a circuit with load sensing and automatic feedback capabilities.

United States Patent 1 Hunter VARIABLE FLUX-RESET FERRORESONANT VOLTAGE REGULATOR [75] Inventor: Patrick L. Hunter, Columbus, Ohio [73] Assignee: North Electric Company, Galion,

Ohio

[22] Filed: Sept. 29, 1971 [21] Appl. No.: 184,763

Related US. Application Data [63] Continuation-impart of Ser. No. 96,380, Dec. 9, 1970,

[11] 3,739,257 June 12, 1973 Primary ExaminerA. D. Pellinen Attorney-Johnson, Dienner, Emrich, Verbeck &

Wagner [5 7] ABSTRACT A thyristor controlled ferroresonant voltage regulator circuit in which the output voltage is made adjustable by varying the reset flux level of each of two parallel magnetic core paths upon which the load windings are wound. One magnetic core path is driven hard into magnetic saturation during one half cycle of the output waveform, and the second magnetic core path is clamped at a given value; in the second half cycle the second path is driven into magnetic saturation and the one path is clamped at the given value. The level of clamping is determined by an associated control circuit which may comprise a simple manually adjustable potential source, or a circuit with load sensing and automatic feedback capabilities.

22 Claims, 16 Drawing Figures LOAD IRCUIT SWI PATENTE JUN 1 2 m3 SHEET 1 0F 6 w T U u c w m R 6% m0 2 0 o A A o o L L JOMPZOU Z w. TVIIJ m 1 F 3 2 S C c v 0 I C l s v FIG. 2

cone SR2 CORE 5R] FIG.5

LOAD CIRCUBT 20 FIG. I-

PAIENIEUJUM 2191s I LOAD CIRCUIT LOAD CIRCUIT PATENIEL' 3.739257 Stiff! 4 [If 6 T2 FIG. I!

NP2 LOAD an Vs T .20

WP! AC 92 aa- -66 saunas 7- *T 90 94 NL/ "'P FEED T, I BACK 5W 5W2 46A CKT. I

mumoL ext 22 FIG. 12'

F IG. 9

MAX/MUM aurpur 4 LOW 53. f? T 1N6 LOW INPUT-L- 7'2 NOMINAL INPUT LOAD man INPUT VOLTAGE LOAD CURRENT PAIENTEU 1 3. 739,257

sum 5 (IF 6 SOURCE 7 LOAD cmcul'r 20 I 72$ 5180 I r I ERROR? INPUT I I 76 RI I I HE IE I FEEDBACK cmcuh' 1mm (CONTROL cuzcurr 22.

FIG. IO

PMWEDJUM 2197s SKEW 5 0F 6 CON TROL MIL VARIABLE FLUX-RESET FERRORESONANT VOLTAGE REGULATOR This application is a continuation-in-part of an application filed by Patrick L. Hunter on Dec. 9, 1970, Ser. No. 96,380, now abandoned, for Variable Flux-Reset Ferroresonant Voltage Regulator.

BACKGROUND OF THE INVENTION The conventional ferroresonant voltage regulator is dependent upon magnetic core characteristics to force the circuit to regulate and hold the output voltage relatively constant for changes in input voltage and load. Such ferro-resonant regulator circuits consist basically of a load circuit, across which is connected a saturable magnetic core and resonating capacitor, and an input circuit which is loosely coupled to the load circuit. It is well known that when the regulator goes into a ferroresonant mode of operation, the saturable core is driven very hard into the saturation flux region of its magnetic characteristic once in each half cycle of the output voltage. The total flux change in the core is therefore limited by the saturation limit of its characteristic. The resonating capacitor is transiently discharged when the core enters the saturation region and resonantly recharges in the opposite polarity. The resultant waveform across the load is trapezoidal, or approaches a square wave and its volt-time area is held relatively constant by the saturating characteristics of the core. The output voltage, as a result, remains relatively constant at a fixed source frequency.

For a given design, it is well known that the output voltage is directly proportional to source frequency since the volt-time area across the core is held constant. It is also well known that the output voltage changes with temperature because the saturation flux density is temperature dependent. Also, the impedances in the load winding and load circuit cause changes in the output voltage when the load current is changed. Manufacturing tolerances in the transformer circuit and tolerances in the saturation flux density of the magnetic core material cause changes in the output voltage for a fixed design. There is no convenient way of adjusting the output voltage or controlling the output voltage to correct for these variables once the design has been made.

Many methods have been applied in an attempt to provide some degree of adjustment or control in the ferroresonant regulator field. One method was described by E. Manteuffel and R. McCary, in The D-C Controlled A-C Voltage Source, A New Magnetic Amplifier, Transaction of AIEE, Vol. 76, 1957, Part I, Communications and Electronics. Another method is described in my copending patent application, Ser. No. 7,670, which was filed Feb. 2, 1970, and assigned to North Electric Company, Galion, Ohio. A disadvantage of the Manteuffel and McCary circuit is that the control is accomplished by a control coil on a selfsaturating magnetic amplifier configuration for the saturating reactor. Such control uses linear amplification techniques to regulate or adjust the output. The circuit disclosed in my copending application is a thyristor controlled circuit utilizing a resonant discharge inductor which is switched in parallel with a resonant capacitor. Such circuit requires two magnetic components, a transformer and a resonant discharge inductor.

SUMMARY OF THE INVENTION An object of the circuit in this invention is to provide a ferroresonant regulator having simplified adjustment or control capabilities, and which further has improved output regulating characteristics. It is a specific object to provide a ferroresonant regulator circuit of such type which requires only one transformer or magnetic component. It is yet another object to provide such type arrangement which uses only switching means to provide a controlled flux level for the different magnetic paths in alternate half cycles to thereby control the output power in the power regulating circuit in a highly efficient manner. I

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of the novel thyristor controlled ferroresonant regulator of the invention;

FIG. 2 is the equivalent circuit for the regulator of FIG. 1 in one condition of operation;

FIG. 3 is a graph of the magnetic characteristics of the cores used in the regulator of FIG. 1;

FIG. 4 is the equivalent circuit for the regulator of FIG. 1 in a second condition of operation;

FIG. 5 is an illustration of one embodiment of a regulator structure in which the load winding is wound on the center leg of the basic core structure;

FIG. 6 is a simplified schematic of the structure shown in FIG. 5;

FIG. 7 is a schematic of a regulator structure which includes the invention, with the load and core windings wound on the outer legs of the structure;

FIG. 8 is a showing of a control circuit which may be used with the structure of FIGS. 1, 2, 4-7, 10, which include and adjustable DC control input;

FIG. 9 is a graph of the load current regulating capabilities of the novel regulators;

FIG'. 10 is a showing of a further embodiment of the novel regulator in which feedback derived from the load is used to improve the regulating characteristics;

FIG. 11 is a schematic showing of a regulator embodiment which has two separate saturable cores, each core having primary and secondary windings wound on the center leg of the core structure;

FIG. 12 is a showing of a basic core structure which is wound for use in the embodiment of FIG. 1'1;

FIG. 13 is a showing of a single core structure which has a primary winding, two load windings and two capacitor windings wound on the center leg of the magnetic core;

FIG. 14 is a schematic showing of a circuit including the core structure of FIG. 13;

FIG. 15 is a graph of the magnetic characteristics of the cores used in FIGS. 11-14; and

FIG. 16 is a further schematic illustrating the manner in which the resonant capacitor may be inductively coupled to the switching elements.

CIRCUIT DESCRIPTION A simplified equivalent circuit of a novel variable flux-reset ferroresonant regulator 10 which utilizes a pair of thyristor switches to control the flux reset level in a pair of saturable cores is shown in FIG. 1. As there shown, the regulator 10 includes a pair of input conductors 14, 16 for connecting an AC source 12 over a series linear inductance L to a circuit 18 consisting of the parallel connection of a resonating capacitor C, a

pair of saturable cores SR1 and SR2 connected across capacitor C with the polarities indicated in the drawings, and a first and a second thyristor SW1 and SW2, each of which is connected across an associated one of the saturable cores SR1, SR2. A control circuit 22 provides gating pulses to the thyristors SW1, SW2 to initiate conduction thereby at a controlled time in each half-cycle of the output voltage. A load circuit 20 which may consist of any arbitrary load, is connected in series with inductance L and across the saturable cores SR1, SR2, and the thyristors SW1, SW2.

In discussing operation of such circuit, it is initially assumed that thyristors SW1 and SW2 are nonconducting. The circuit therefore reduces, essentially, to an equivalent circuit in which the series connection of saturable cores SR1 and SR2 form a saturable reactor SR. In this form, the circuit operates as a simple ferroresonant regulator commonly understood in the power supply field. With positive voltage applied to the dotted terminals, the flux in saturable cores SR1 and SR2 is driven hard into positive saturation toward the end of the positive half cycle of the load voltage, and into negative saturation toward the end of the negative half cycle of the load voltage. The total flux-density change AB in the cores is equal to 2 B m where B m is the maximum flux density in the saturation region of the core.

The instantaneous voltage across capacitor C is the sum of v and v and can be written as where N and N are the winding turns of saturable cores SR1 and SR2 respectively, and d), and 4 are the instantaneous flux levels in saturable cores SR1 and SR2 respectively. For identical coils and magnetic cores N N N we can show that the rectified average voltage E across capacitor C is where f is the source frequency and A45 Adz are the flux changes in cores SR1 and SR2. This equation as written in terms of flux density, and assuming the effective core areas A are equal, reads E 2fNA (AB, =AB2) where A13 and A13 are the flux-density changes in saturable cores SR1 and SR2. If A3,, A5 or both, are changed, therefore, the voltage E will change.

With reference to FIG. 1, thyristors SW1 and SW2 which are connected across saturable cores SR1 and SR2 are controlled by utilizing control circuit 22 which adjusts the firing of thyristors SW1 and SW2 to control the flux change. The capacitor C is resonantly discharged and reversed in polarity by the saturation of one of the cores.

It is first assumed that v, is positive and thyristor. SW1 is gated into conduction whereby the voltage V is applied across saturable core SR2 and thyristor SW2 is reverse biased. The equivalent circuit (assuming zero voltage across conducting thyristor SW1) is shown in FIG. 2. As will be shown, the flux in core SR1 is clamped at a fixed value when thyristor SW1 conducts, but the flux in saturable core SR2 increases in a positive direction toward saturation. Moreover, when core SR2 enters saturation, the capacity C begins to resonantly discharge and to reverse polarity due to the low saturation inductance of the saturable core SR2.

Using an idealized B-I-l magnetic characteristic for the cores, the flux levels are shown in FIG. 3 at the point where the voltage v crosses zero and the flux in saturable core SR2 is maximum at a value +5 When the current in saturable core SR2 passes through zero shortly after the voltage v goes negative, thyristor SW1 becomes non-conductive, and the flux in both saturable cores SR1, SR2 decreases toward more negative values until such time as thyristor SW2 is fired into conduction. At this time, the voltage across saturable core SR2 becomes zero and the flux in saturable core SR2 alone is clamped at a negative value B The voltage v,, is now applied across saturable core SR1, and the flux in saturable core SR1 continues to decrease toward negative saturation.

The equivalent circuit when thyristor SW2 is conducting is shown in FIG. 4. When saturable core SR1 enters the saturation region, the capacitor C resonantly discharges and recharges in the positive direction. When the voltage V, crosses zero, the flux in saturable core SR1 reaches its maximum negative value B Shortly after the voltage v, becomes positive, thyristor SW2 becomes non-conducting, and the flux in both cores increases toward more positive values and the cycle repeats.

The flux levels [3 and [3 are the reset-flux values which are controlled by firing of the respective thyristors SW1, SW2. The total flux changes AB and A13 are:

B! BIS and 1 2 B211 B29 It is, therefore, theoretically possible to reduce the output voltage E to zero by firing the thyristors SW1, SW2 as soon as the anode voltage becomes positive, thus limiting AB, and A13 to zero flux change. It is apparent that wide ranges of adjustment are possible.

Briefly summarized, while both core paths are driven toward magnetic saturation during each half cycle of the output waveform, only one of the saturable cores is driven into hard saturation during one half cycle and the other saturablecore is clamped at a fixed level. In the next half cycle the other saturable core is driven into hard saturation and the one core is clamped at the fixed level. Control of the signal input to the thyristors SW1, SW2 determines the time that the appropriate thyristor will turn on in a given half cycle and thereby the level at which the flux will be clamped in its associated core. The flux level which is thus selected determines the value of the output voltage across the load.

The control is symmetrical and results in output waveforms having only odd harmonics. It is possible to control the output by firing only one of the thyristors and letting the other remain non-conducting. This results in output voltage control from approximately fifty percent to one hundred percent of the maximum obtained when both thyristors are non-conducting; however, unsymmetrical operation occurs and even harmonics are present in the output waveform. In a rectifier-filter application, unbalance-in ripple voltage across the filter would limit the use of such arrangement. The decouplinginductance L provides current limiting and protection from overload in the manner of the conventional ferro-resonant transformer regulator circuit.

Regulator Circuit Structure The regulator circuit operation set forth in the foregoing description can be achieved by different types of circuit structures which reduce to the simplified equivalent circuit shown in FIG. 1... Certain preferred ones of such embodiments are now set forth.

As will be apparent, in each instance, the basic structure includes two magnetic flux paths as shown in FIG. 5, and the load voltage E and capacitor voltage E are proportional to the summationof the rate of change of flux in each of the flux paths.

With reference now to FIG. 5, there is shown thereat astructural arrangement which comprises a one-piece ferro-resonant transformer structure 30 having a threelegged core comprised of stacked iron laminations. In one preferred embodiment the structure comprises conventional E configuration laminations disposed to form an upper transverse leg 34, vertical side legs 36, 38 and a vertical center leg 40. I-shaped laminations are disposed to abut and span the open end of the E- shaped laminations so as to provide lower transverse leg 42. The E-I laminations may be interleaved in known manner to form the structure as shown in FIG. 5.

Magnetic shunts 44A, 44B are located in abutting relation to the center vertical leg 40 with the ends thereof located in spaced adjacent relation to vertical legs 36, 38 to provide air gaps 45, 46 respectively.

A primary winding N, is wound on the vertical center leg 40 above the magnetic shunts 44A, 44B and the ends thereof are connected over terminals 50, 52 and conductors 14, 16 to a conventional AC source 12. A load winding N wound on the center leg 40 of transformer 30 is connected to the load circuit 20, and a capacitor winding NC wound on the center leg 40 is connected to resonant capacitor C. Windings N1, N2 are wound respectively at the lower ends of outer legs 38, 36, and are connected over the anode-cathode path of thyristors SW1, SW2 respectively. The control elements of thyristors SW1, SW2 are connected to the output of control circuit 22.

The instantaneous flux levels in the saturable core paths are indicated by the arrows in FIG. 5, the

outer legs 36, 38 forming a part of the two parallel flux paths for the novel regulator circuit. A simplified circuit schematic of such arrangement is shown in FIG. 6 and like parts are identified by like numbers.

A further embodiment of the novel circuit wherein the load winding N and core windings N N are wound on the outer legs is shown in FIG. 7. With reference thereto, it will be apparent that the physical structure and circuit schematic are similar to that shown in FIGS. 5 and 6 with the exception that the load circuit winding N now comprises a first and a second winding N N which are wound on outer legs 36, 38 respectively, whereby the load is derived by the sum of the voltages across windings N and N Also capacitor C in this embodiment is connected across windings N N wherebythe capacitor voltage E is the sum of the voltages across windings N and N which are wound on outer legs 36, 38.

As an alternative arrangement to the double load winding shown in FIG. 7, a single load winding N may be wound on the center leg 40 in the manner of the structure shown in FIG. 5. Such arrangement, a long with other like variations, is believed to be within the spirit and scope of the present invention.

Operation of each of the different circuit arrangements set forth above will be apparent from the basic theory of operation which has previously been set forth. Briefly, in each of these circuits a basic one piece magnetic structure is controlled by a pair of thyristor switches and associated control circuit to provide a regulator which is adjustable by manual or feedback means. In either mode, the adjust capability is achieved by varying the reset flux level in each of the two parallel magnetic core paths upon which the load windings are wound, the flux level for the two different core paths being reset during alternate half cycles. When one core path is reset, the other core path is being driven towards saturation. The resultant load voltage and capacitor voltage are proportional to the sum of the voltages across windings N and N since the flux which couples the load and capacitor windings is the sum of the flux values 4), and in the parallel magnetic paths (assuming no other leakage flux paths). The load voltage at which regulation occurs may be changed by manually adjusting a bias potential in control circuit 22 for the thyristors SW1, SW2 which changes the time of conduction of the switches in the respective half cycles and thereby the reset flux level) or by utilizing a feedback circuit which senses load voltage to provide automatic adjustment of the thyristor operation.

Control Circuit One basic control circuit 22 which may be used with the novel regulators is shown in FIG. 8. In the control of these regulators for a given adjust value it is desirable to maintain a ferroresonant mode of operation. In the present disclosure, such type response is achieved by the use of a simple integrator circuit and a level detector and amplifier circuit.

With reference to FIG. 8 one embodiment of a control circuit 22 is shown thereat. A voltage v; which is proportional to the load voltage is derived by a pair of control windings N N wound on the outer legs 36, 38 of transformer 30 (described more fully hereinafter).

Such voltage v, is fed over an integrating circuit, com

prised of resistor R1 and capacitors C1, C2 and diodes D1, D2, to the base input for a transistor Q1 which is connected as a first level detector and amplifier transistor, and which has its output connected to provide gating current over resistor R3 to the control gate for thyristor SW2 of the associated regulator (i.e., the regulator in FIG. 7 for example).

The integrating circuit also drives a transistor Q2 which is connected as a second level detector and amplifier to provide gating current over resistor R2 to thyristor SW1 of an associated regulator.

A first adjustable DC source 46 has its negative terminal connected common to the emitters of transistors Q1, Q2 and its positive terminal connected to the junction of diodes D1, D2. Diode D1 is connected across capacitor C1 to clamp the base of transistor O1 to the positive voltage terminal of source 46, and diode D2 is connected across capacitor C2 to clamp the base of transistor O2 to the positive voltage terminal of source 46.

A further DC bias source 48 has its positive terminal connected to the positive terminal of the first source and its negative terminal connected over resistors R5 and R4 to the collectors of transistors Q1, Q2 respectively.

As the feedback voltage v, is applied to the input for the control circuit 22, integrator circuits R1, C1 and R1, C2 provide integrated voltages across capacitors C1 and C2. The integrated voltages on capacitors C1, C2 are applied to the base of transistors Q1, Q2 respectively which compares the same with the reference signal input to the emitter thereat by adjustable source 46.

It will be apparent that with an increased input DC reference signal'transistors Q1 and Q2 control the thyristors SW1, SW2 to function at later intervals in their respective half cycles and the flux level in the associated cores will be increased. With such increase in the core flux level the output voltage to the load is increased by a proportional amount. A decrease in value of the DC reference input signal results in a corresponding decrease in the value of the output voltage to the load.

As noted above, the DC control input 46 may be manually adjustable, or alternatively, may comprise a feedback amplifier path which senses output voltage, and provides signals at the control input to maintain the output more finely regulated.

A typical control characteristic which shows the adjust and regulating capability of the novel regulator is shown in FIG. 9, The illustrative curves illustrate the regulation provided for line voltage and load current variations for a given DC control input. Maximum output is obtained for maximum value of the DC control input and is determined strictly by the saturation limits of the magnetic cores. The thyristors are nonconducting at this output setting. A lower adjust setting is achieved by reducing the DC control input voltage. At a constant DC control input the regulator provides line and load regulation, as shown in FIG. 9, and functions exactly like a conventional ferroresonant regulator with respect to its terminal characteristics.

The regulator output voltage is directly proportional to source frequency for a constant DC control input. The DC control can be varied by feedback techniques to improve regulating characteristics for line, load, temperature and frequency.

A regulator circuit utilizing a feedback amplifier which derives an input from a voltage signal across the load terminals, is shown in FIG. 10. This configuration will provide a very closely regulated output voltage for all variables (source, load, temperature, etc).

With reference thereto, it will be seen that the basic circuit arrangement of the regulator shown in FIG. is the same as that shown in FIGS. 7 and 8 with the exception that the manually adjustable DC control input of FIG. 8 is replaced by a feedback circuit 46A. In addition the control circuit 22 and load circuit 20 are shown in more detail.

In brief detail, the three-legged magnetic transformer structure 30 locates a primary winding N, wound on the upper end of the middle leg 40, which winding is connected over terminals 50, 52 and conductors 14, 16 to an AC source 12. A pair of load windings N N wound on the outer legs 36, 38 respectively are connected in series to the two input terminals of a full wave rectifier 60 in load circuit 20. The output terminals of rectifier 60 are connected to a load 64 and a filter capacitor 62 is connected across such output.

A feedback circuit 46A has a pair of voltage sensing conductors 66, 68 connected across the load 64 to provide an input to a divider network comprised of resistors 76, 78, 80. A negative feedback amplifier and detector 74 which may comprise a linear amplifier circuit having voltage and power gain which has one of its inputs connected to an adjustable arm on resistor 78. A

second input of the linear amplifier is connected to a source of fixed reference potential which is derived at the junction of Zener diode and resistor 72 which are serially connected across the load. The output from linear amplifier 74 which varies as a function of the voltage output is connected as a reference signal input for control circuit 22 (i.e., to replace the manually adjustable source 46 of FIG. 8). It will be apparent that the reference signal input to amplifier 74 represents a voltage proportional to the load voltage at which regulation is to occur, and that with variation of the load voltage from a preset value, the error input over conductors 66, 68 will result in a proportional difference signal input to amplifier 74 and a corresponding change in the DC signal input to the control circuit 22.

Control windings N N. wound on outer legs 36, 38 respectively provide the AC control input (v,) to con-' trol circuit 22. Such signals are integrated by integrating circuit R1, C1, C2 and applied to the bases of transistors Q1, Q2 respectively. Whenever the integrated voltages applied to the base terminals of transistors Q1, Q2 exceed the DC reference signal obtained from the feedback circuit 46A, transistor Q1 (or transistor Q2, as the case may be) will conduct to provide a gating signal over conductor R3 (or R2) to the gate for the associated thyristors SW1, SW2. Variation in the feedback signal as the result of a changing output voltage effects a corresponding change in the time of the gating pulse in each half cycle, and accordingly the time of conduction of said thyristors in such half cycle. A change in time of conduction of the thyristors in their respective half cycles results in a corresponding change in the reset flux level in the outer legs 36, 38 to correspondingly adjust the voltage in the load windings N N That is, as the conduction of the thyristors occurs later in its half cycle, the flux level increases, and the voltage output is likewise increased. Correspondingly, as the error signal difference decreases, the time of conduction of the thyristors occurs earlier in the half cycle and the flux level decreases to decrease the output voltage. As noted above, such mode of operation, in addition to utilizing a basic, simple control arrangement, is highly efficient.

In a further embodiment shown in FIG. 1 l, the ferroresonant voltage regulator comprises a first and a second transformer structure T T each having an associated input primary winding N N wound on saturable cores SR SR respectively. The primary winding N N of the separate transformers T T as shown are connected in parallel across an AC source by conductors 91, 92.

Transformer T also comprises a first load winding N and a first capacitor winding N wound on core SR, and a magnetic shunt 94 which is located on saturable core SR to loosely couple the secondary windings N,, N to the primary winding N,,,.

In a similar manner, the second transformer T includes a load winding N and a capacitor winding N wound on the saturable core SR and a magnetic shunt 96 located on core SR to loosely couple the secondary windings N N to the primary winding N The secondary windings N N of transformer T T are connected in series to supply current to load circuit 20, and secondary windings N and N are connected in series with a resonating capacitor C.

A first thyristor device SW1 is connected across core or capacitor winding N and a second thyristor device SW2 is connected across core or capacitor winding N whereby each thyristor device SW1, SW2 as enabled by gating signals from an associated control circuit 22 will short its associated windings N and N, at controlled times in each half-cycle of the load voltage. Control circuit 22 (and the associated feedback circuit 46A) which is connected across load 20 by conductors 66, 68 may be of the type shown in detail in FIG. 10.

In operation, each ferroresonant transformer T T supplies one half the total output power. That is, the resonating capacitor voltage is comprised of the sum of the voltages across windings N and N and the output voltage to the load 20 consists of the sum of the voltages across windings N and N Two magnetic core structures, each of which is similar to that shown in FIG. 5, may be used for each of the transformers T T illustrated in FIG. 11. With refer ence to FIG. 12, one such magnetic structure is shown thereat as wound to provide the first transformer T As there shown, the primary winding N is wound on the center leg above the magnetic shunt 94, and the secondary load windings N and N, are wound on the center leg below the magnetic shunt 94. It will be understood that a similar structure would also be provided for transformer T and that the windings of the two transformers T, and T would be interconnected as shown in FIG. 11.

The novel two-transformer regulator circuit and structure of FIGS. 11 and 12 may be included in a single structure in the manner shown in FIG. 13. With reference thereto, such regulator is shown to comprise a one piece transformer structure comprising a three legged core of stacked iron laminations. In the illustrated embodiment, conventional E configuration laminations are disposed to provide an upper transverse leg 34', vertical side legs 36, 38 and a vertical canter leg 40. l-shaped laminations are disposed to abut and span the one end of the E shaped laminations so as to provide lower transverse leg 42. The E-I laminations are interleaved in known manner to form the illustrated structure.

Magnetic shunts 94, 96 are" located in spaced relationship on the center vertical leg 40' with the ends thereof located in spaced adjacent relation to vertical legs 36, 38' to provide air gaps 93, 95 and 97, 98 respectively.

A single primary winding N, is wound on the central portion of center leg 40' between the shunts 94, 96 and as shown in FIG. 14 is connected across an AC source 90 by conductors 101, 102. A secondary coil structure consisting of capacitor winding N, and a load winding N are wound on the lower portion of center leg 40' between the lower transverse leg 42 and magnetic shunt 94, the magnetic shunt 94 thereby providing a loose coupling between primary winding N, and the secondary windings N N A second capacitor winding N and a second load winding N are wound on the upper portion of the center leg 40' between the magnetic shunt 96 and the upper transverse leg 34, the shunt 96 providing a loose coupling between secondary windings N,, N and theprimary winding N,,.

With reference to FIG. 14, it will be apparent that as in FIG. 11, the load windings N N L2 are connected in series to load circuit 20 and the capacitor windings N N are connected in series across resonating capacitor C. Thyristor SW1 is connected across capacitor winding N and thyristor SW2 is connected across capacitor winding N Control circuit 22 (and a feedback circuit 46A if desired) are connected to control the thyristor SW1 and SW2 as in FIG. 11.

OPERATION The magnetic circuit of the FIGS. 11-14 consists of two magnetic paths through which flux 5, and (15 can flow independently of each other and independent of the primary flux (b Essentially this means that there are three independent flux paths. In this case dz, is established by the source voltage v, and is given by Flux values 4), and are controlled by the secondary circuit which consists of the resonant capacitor C, thyristors SW1, SW2 and the associated controlcircuit 22, and capacitor windings N, and N The difference flux values, (b, (b, and 5, are forced to flow over the magnetic shunts 94, 96.

With the thyristors SW1 and SW2 in a nonconducting state, the regulator circuit functions in a manner similar to a conventional ferroresonant regulator, wherein the secondary windings, such as N N of two ferroresonant transformer circuits are connected in series. The flux-density values B and B (rial/A or arrangement shown in 2/A) vary over the limits shown in FIG. 15 of B to +8 for core SR1 and -B to +3 for core SR2.

The resultant output voltage is proportional to the sum of the flux-density changes 2B,, and 2B in each core. Each core is driven hard into magnetic saturation once in each half-cycle as shown in FIG. 15. By controlling the interval of firing of thyristor SW1 and SW2 in each half cycle the flux change in each core can be varied.

It is initially assumed that at some time in the halfcycle of the output waveform, when the dotted terminals are positive, both thyristors SW1,'SW2 are nonconducting, and that the flux-density in each core portion SR1, SR2 is increasing in a positive direction. When the flux-density in core portion SR2 reaches the value +B thyristor SW2 is gated into conduction which effectively short circuits winding N and clamps the flux density at that value. No further flux change in core portion SR is possible while thyristor SW2 is conducting; however, the flux-density in core portion SR, is increasing toward positive saturation and a maximum value +B,

When core portion SR1 enters the saturation region, the resonant capacitor C discharges through the circuit path consisting of thyristor SW2 and winding N due to the low saturation inductance of winding N The voltage of capacitor C thereupon reverses polarity and charges to a large negative voltage. When the current in thyristor SW2 goes to zero, it becomes nonconducting. The flux-density in core portion SR2, as a result, starts to change in a negative direction.

At some later time in the negative half-cycle thyristor SW1 is gated into conduction, which effectively short circuits winding N and clamps the flux-density at a value --B,,;. The flux-density in core region SR continues to change toward negative saturation and a maximum value B When core portion SR enters the saturation region, the resonant capacitor C discharges through the circuit path consisting of thyristor SW1 and winding N due to the low saturation inductance of winding N The voltage of capacitor C reverses polarity and charges to a large positive voltage. When the current in thyristor SW1 goes to zero, thyristor SW1 becomes nonconducting. A complete cycle has now been completed.

The total load voltage V and the resonant capacitor voltage V are waveforms identical to the conventional ferro-resonant regulator waveforms.

The resonant capacitor C and thyristor circuit including thyristors SW1, SW2 are shown directly coupled in the embodiment shown in FIG. 14. However, as shown in FIG. 16, the resonant capacitor C may be inductively coupled to the thyristors SW1, SW2. In such arrangement, additional windings N N are provided on the core structure adjacent windings N N and the resonant capacitor C is connected in series with the windings N N The thyristors SW1, SW2 are connected to the windings N N as in the embodiment of FIG. 13.

Control of the firing of thyristors can be achieved in the open loop mode of FIG. 8 or the feedback loop mode of FIG. 10. In each mode, feedback windings,

such as N N supply voltage inputs to an integrator circuit including resistance and capacitance R C C The output from the integrator circuit R C C is compared with the reference voltage E input to the level detector circuit including transistors Q Q. When the integrated voltages provided by integrator circuit R C C becomes equal to the voltage E,,, the appropriate one of the transistors Q Q will turn on to provide a firing pulse to the gate of the appropriate thyristor SW1, SW2.

In the structural arrangement shown in FIGS. 11-16, the mounting of the coils on the center leg reduces the strength of stray magnetic fields which may be experienced in the embodiments in which the secondary windings are wound on the outer legs, and thereby minimizes the need for and the problem of shielding which might otherwise be required for certain types of applications. If shielding is desired, it is further possible to add extra iron areas to the outside legs in the arrangement shown in FIGS. 11-16. In addition, the mounting of the coils on the center leg makes manufacture of the unit somewhat less difficult and results in a corresponding cost saving.

Finally, the location of the secondary coils on the I center leg rather than on the outside legs can result in a reduction of the copper wire requirements. That is, the secondary windings when mounted on the two outside legs normally result in a larger effective mean turn length of copper. Accordingly, in certain embodiments the illustrated arrangement of FIGS. 13 and 14 may be preferred.

ADDENDUM Multiple outputs are easily obtained by use of multiple output windings, rectifiers and filters. The transformer output can be regulated by regulating a voltage proportional to the sum of the rates of change of flux in each parallel magnetic path. A small sense winding can be wound on each core, the two windings connected in series, and the resultant voltage rectified, filtered and compared with a reference voltage. The resultant error signal, if amplified, can be used as a correcting DC control input to the thyristor control cir- While what is described is regarded to be a preferred embodiment of the invention, it will be apparent that variations, rearrangements, modifications and changes may be made therein without departing from the scope of the present invention as defined by the appended claims.

I claim:

1. In a regulator device, a transformer structure having a magnetic core which has at least a first and a second magnetic core path, a primary winding wound on said magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means on said magnetic core including load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said first and second magnetic paths, means for decoupling said source from said load winding, a first core winding for said first magnetic path and a second core winding for said second magnetic path, capacitor means coupled across said first and second core windings, and a first switching means coupled across said first core winding operative as enabled in a first half cycle of the load voltage to selectively couple said capacitor means across said second core windings to drive said second magnetic core path into hard magnetic saturation, said first switch means being further operative as enabled to clamp the flux in the first one of said magnetic core path at a value which varies with and-is determined by the time in the half cycle at which said first switching means is enabled, and a second switching means coupled across said second winding operative in the second half cycle of the load voltage to selectively couple said capacitor means across said first magnetic core path to drive said first magnetic core path into hard magnetic saturation and to clamp the flux level in the second magnetic core path at a selected value which is determined by and varies with the time in said second half cycle at which said switching means is enabled.

2. A regulator device as set forth in claim 1 which includes adjustable means for selectively varying the time of enablement of said switching means in their respective half cycles of operation.

3. A regulator device as set forth in claim 2 in which said adjustable means comprise a variable DC potential source which is manually adjustable.

4. A regulator device as set forth in claim 2 in which said adjustable means controls enablement of said first and second switching means at later intervals in their respective half cycles to increase the flux level in said first and second magnetic paths and thereby increase the output voltage.

5. A regulator device as set forth in claim 1 which includes a feedback circuit including first means connected to sense the value of the load voltage, and second means for providing an error signal representative of the difference between a desired voltage value and the value sensed by said first means, and control means including an integrating circuit for providing signals proportional to the integral of said output voltage, and means for comparing said error signal and said signal output of said integrating circuit, and means responsive to the difference of said signals for controlling said switching means to effect a corresponding adjustment in the level at which the flux is clamped to thereby adjust the voltage output in a related manner.

6. A regulating device as set forth in claim 1 which includes means for deriving an AC signal related to the flux in said first and second magnetic paths, and means for providing a first DC signal indicating the value at which regulation is to be provided, and control means including integrating means for providing a second signal having a value related to the AC signal, and means for controlling said switching means to clamp the flux level in the first and second magnetic paths at a time interval in the respective half cycles which is determined by the relative values of said first and second signals.

7. A regulator device as set forth in claim 1 in which the rec tified average voltage F across said load winding is E. 2f NA (A13 lAB2) Where A3 A3 are the flux density changes in the cores supporting said first and second core windings, f is the source frequency, N is the number of turns in the core windings and A is the effective area of said core, and in which said switching means are operative to adjust the reset flux levels +3 and netic paths to different values to provide the desired regulation of voltage E}.

8. In a regulator device, a transformer structure having a magnetic core which has first and second magnetic paths, primary winding means wound on said magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means on said magnetic core including load winding means wound on said core for providing an output voltage proportional to the rate of change of flux in said first and second paths, and a first core winding for said first magnetic path and a second core winding for said second magnetic path, means for decoupling said source from said load winding, capacitor means coupled across said first and second core winding, switching means including a first switch means connected across said first core winding operative as enabled to control current conduction from said capacitor over the second core winding to drive said second magnetic core path into hard magnetic saturation and said first switch means being further operative to clamp the flux in said first magnetic core path at a level which varies with and is determined by the time in the half cycle at which said first switch means is enabled, and a second switch means coupled across said second core winding operative as enabled to control current conduction from said capacitor over said first core winding to drive said first magnetic core path into hard magnetic saturation and to clamp the flux in said second magnetic core path at a level which is determined by and varies with the time in a second half cycle at which said second switch means is enabled, and control means for selectively enabling said first and second switch means at selected variable times in alternate half cycles.

9. A regulator device as set forth in claim 8 which includes means for providing a first signal input to said control means, and which includes a reference source for providing a second signal which indicates the regulation desired, and mans in said control means for controlling said switch means in said regulator in accordance with the relative value of said first and second signals.

10. A regulator device asset forth in claim 8 in which said first and second switch means are thyristors, and said control means include a manually adjustable DC -B in said first and secondmag potential source for adjustably providing different reference signals to said thyristors to thereby vary the firing time of the thyristors and the level of clamping of the flux in each half cycle.

11. A regulator device as set forth in claim 8 in which said magnetic core provides first and second magnetic paths which are in parallel in a portion of said core, and said load winding means comprises a first winding wound on the transformer magnetic core portion which includes said first parallel magnetic path and a second winding wound on the transformer magnetic core portion which includes said second parallel magnetic path.

12. A regulator device as set forth in claim 8 which includes means for providing a reference signal indicating the value at which regulation is to be provided, and in which said control means includes winding means wound on the portions of said magnetic core which includes said first and second magnetic paths, integrator means for integrating the waveforms provided by said winding means, and gating means for providing gating signals to said switch means at a time in each half cycle which is determined by the relative value of the reference signal and the integrated signal.

13. A regulator device as set forth in claim 12 in. which said gating means includes a first and second transistor, each of which is controlled by said integrated and reference signals to provide a gating signal output during a different half cycle to an associated one of said first and second switch means.

14. In a regulator device, a magnetic core having first and second magnetic core paths including first and second side vertical legs, a center vertical leg, and an upper and lower transverse leg, a primary winding wound on said center leg, means for connecting said primary winding to an alternating current source to provide flux in said first and second magnetic core paths on said magnetic core, load winding means wound on said magnetic core for providing an output voltage to a load, means for decoupling said source from said load, a first core winding wound on the portion of said core including said first magnetic core path and a second core winding wound on the portion of said core including said second magnetic core path, capacitor means coupled across said first and second core windings, a pair of switches, each of which is connected across a different one of said first and second core windings, the one switch for the first core winding being operative as enabled to selectively couple said capacitor means across the second core winding to drive the second magnetic core path into hard magnetic saturation and to clamp the flux in the first magnetic core path at a value which is determined by and varies with the time in a half cycle of the output voltage at which said one switch is enabled, and the other switch of said pair being operative as enabled to selectively couple said capacitor means across the first core winding to drive the first magnetic core path into hard magnetic saturation and to clamp the flux in the second magnetic path at a value which is determined by and varies with the time in an alternate half cycle of the output voltage at which the other switch is enabled, and control means for gating a different one of said switches into conduction at a selected time interval in alternate half cycles of the load voltage waveforms;

15. A regulator device as set forth in claim 14 in which said load winding means comprises one load winding wound on said center vertical leg.

16. A regulator device as set forth in claim 14 in which said load winding means comprises a first winding wound on the first of said side vertical legs and a second load winding wound on the second of said side vertical legs.

17. A regulator device as set forth in claim 14 which includes a capacitor winding wound on said center leg, and in which said capacitor means are connected to the output of said capacitor winding.

18. A regulator device as set forth in claim 14 in which each switch of said pair is operative as enabled to clamp the flux level in a corresponding one of aid paths, and which includes adjustable means for providing a reference signal'to said control means indicating the value at which regulation is to be provided, and in which said control means adjusts the time of conduction by said switches to change the flux level in the first 'and second parallel magnetic core paths at which clamping occurs to thereby achieve the desired regulation.

19. In a regulator device, a transformer structure having a magnetic core which has a center leg over which first and second magneticpaths are established, primary winding means wound on said center leg of the magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means including load winding means wound on said center leg of said core for providing an output voltage proportional to the rate of change of flux in said first and second paths, a first core winding wound on said center leg for said first magnetic path and a second core winding wound on said center leg for said second magnetic path, magnetic shunt means for decoupling said source from said secondary windings, capacitor means coupled across said first and second core windings, switching means including a first switch means coupled across said first core winding to control current conduction from said capacitor over the second core path to drive said second magnetic core path into hard magnetic saturation and to clamp the flux in said first magnetic core path at a selected level which varies with and is determined by the time in a first half cycle of the output voltage at which said first switch means is enabled, and a second switch means coupled across said second winding to control current conduction from said capacitor over said first core path and to clamp the flux level in said second core path at a selected level which is determined by and varies with the time in a second half cycle of the output voltage at which said second switch means is enabled, and control means for selectively enabling said first and second switch means in alternate half cycles.

20. A regulator device as set forth in claim 19 in which said load winding means includes a first and a second load winding and in which said means for decoupling said source from said secondary windings comprising a first and second magnetic shunt member located on said center leg, and in which said primary winding is wound on said center leg between said first and second shunt members, and a first one of said load windings and a first one of said core windings are located on said center leg between the first magnetic shunt and one end of said center leg and the second one of said load windings and the second one of said core windings are located on said center leg between the second magnetic shunt and the other end of said center leg.

21. In a regulator device, a first transformer having a first magnetic core which has a first magnetic path, a first primarywinding wound on said first magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means wound on said first magnetic core including first load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said first magnetic path, and a first core winding for said first magnetic path, and means for decoupling said first primary winding from said second.- ary winding means; a second transformer having a second magnetic core which has a second magnetic path, a second primary winding wound on said second magnetic core including means for connecting said second primary winding to said alternating current source in parallel with said first primary winding, secondary winding means wound on said second core including second load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said second magnetic path, and a second core winding for said second magnetic path, magnetic shunt means for decoupling said source from said further secondary winding means, capacitor means coupled across said first and second core windings, and switching means including a first switch means as enabled in only a first half cycle of the load voltage to selectively couple said capacitor means across the second one of said core windings to drive said second magnetic path into hard magnetic saturation by said capacitor means and to clamp the flux level in the first one of said magnetic paths at a selected value which varies with and is determined by the time in the first half cycle at which said first switch means is enabled, and a second switch means coupled across said second winding operative as enabled in a second half cycle of the load voltage to selectively connect said capacitor means across the first core winding to drive said first magnetic path into hard magnetic saturation and to clamp the flux level in the second one of said magnetic paths at a value which varies with and is determined by the time in the second half cycle at which said second switch is enabled, and control means for selectively gating a different one of said first and second switch means in each half cycle.

22. A regulator device as set forth in claim 21 in which each of said transformers include a center leg, and the primary and secondary windings for each transformer are wound on its center leg. 

1. In a regulator device, a transformer structure having a magnetic core which has at least a first and a second magnetic core path, a primary winding wound on said magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means on said magnetic core including load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said first and second magnetic paths, means for decoupling said source from said load winding, a first core winding for said first magnetic path and a second core winding for said second magnetic path, capacitor means coupled across said first and second core windings, and a first switching means coupled across said first core winding operative as enabled in a first half cycle of the load voltage to selectively couple said capacitor means across said second core windings to drive said second magnetic core path into hard magnetic saturation, said first switch means being further operative as enabled to clamp the flux in the first one of said magnetic core path at a value which varies with and is determined by the time in the half cycle at which said first switching means is enabled, and a second switching means coupled across said second winding operative in the second half cycle of the load voltage to selectively couple said capacitor means across said first magnetic core path to drive said first magnetic core path into hard magnetic saturation and to clamp the flux level in the second magnetic core path at a selected value which is determined by and varies with the time in said second half cycle at which said switching means is enabled.
 2. A regulator device as set forth in claim 1 which includes adjustable means for selectively varying the time of enablement of said switching means in their respective half cycles of operation.
 3. A regulator device as set forth in claim 2 in which said adjustable means comprise a variable DC potential source which is manually adjustable.
 4. A regulator device as set forth in claim 2 in which said adjustable means controls enablement of said first and second switching means at later intervals in their respective half cycles to increase the flux level in said first and second magnetic paths and thereby increase the output voltage.
 5. A regulator device as set forth in claim 1 which includes a feedback circuit including first means connected to sense the value of the load voltage, and second means for providing an error signal representative of the difference between a desired voltage value and the value sensed by said first means, and control means including an integrating circuit for providing signals proportional to the integral of said output voltage, and means for comparing said error signal and said signal output of said integrating circuit, and means responsive to the difference of said signals for controlling said switching means to effect a corresponding adjustment in the level at which the flux is clamped to thereby adjust the voltage output in a related manner.
 6. A regulating device as set forth in claim 1 which includes means for deriving an AC signal related to the flux in said first and second magnetic paths, and means for providing a first DC signal indicating the value at which regulation is to be provided, and control means including integrating means for providing a second signal having a value related to the AC signal, and means for controlling said switching means to clamp the flux level in the first and second magnetic paths at a time interval in the respective half cycles which is determined by the relative values of said first and second signals.
 7. A regulator device as set forth in claim 1 in which the rectified average voltage Ec across said load winding is Ec 2f NA ( Delta Beta 1 + Delta Beta 2) 10 8 where Delta Beta 1, Delta Beta 2 are the flux density changes in the cores supporting said first and second core windings, f is the source frequency, N is the number of turns in the core windings and A is the effective area of said core, and in which said switching means are operative to adjust the reset flux levels + Beta 1R and - Beta 2R in said first and second magnetic paths to different values to provide the desired regulation of voltage Ec.
 8. In a regulator device, a transformer structure having a magnetic core which has first and second magnetic paths, primary winding means wound on said magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means on said magnetic core including load winding means wound on said core for providing an output voltage proportional to the rate of change of flux in said first and second paths, and a first core winding for said first magnetic path and a second core winding for said second magnetic path, means for decoupling said source from said load winding, capacitor means coupled across said first and second core winding, switching means including a first switch means connected across said first core winding operative as enabled to control current conduction from said capacitor over the second core winding to drive said second magnetic core path into hard magnetic saturation and said first switch means being further operative to clamp the flux in said first magnetic core path at a level which varies with and is determined by the time in the half cycle at which said first switch means is enabled, and a second switch means coupled across said second core winding operative as enabled to control current conduction from said capacitor over said first core winding to drive said first magnetic core path into hard magnetic saturation and to clamp the flux in said second magnetic core path at a level which is determined by and varies with the time in a second half cycle at which said second switch means is enabled, and control means for selectively enabling said first and second switch means at selected variable times in alternate half cycles.
 9. A regulator device as set forth in claim 8 which includes means for providing a first signal input to said control means, and which includes a reference source for providing a second signal which indicaTes the regulation desired, and mans in said control means for controlling said switch means in said regulator in accordance with the relative value of said first and second signals.
 10. A regulator device as set forth in claim 8 in which said first and second switch means are thyristors, and said control means include a manually adjustable DC potential source for adjustably providing different reference signals to said thyristors to thereby vary the firing time of the thyristors and the level of clamping of the flux in each half cycle.
 11. A regulator device as set forth in claim 8 in which said magnetic core provides first and second magnetic paths which are in parallel in a portion of said core, and said load winding means comprises a first winding wound on the transformer magnetic core portion which includes said first parallel magnetic path and a second winding wound on the transformer magnetic core portion which includes said second parallel magnetic path.
 12. A regulator device as set forth in claim 8 which includes means for providing a reference signal indicating the value at which regulation is to be provided, and in which said control means includes winding means wound on the portions of said magnetic core which includes said first and second magnetic paths, integrator means for integrating the waveforms provided by said winding means, and gating means for providing gating signals to said switch means at a time in each half cycle which is determined by the relative value of the reference signal and the integrated signal.
 13. A regulator device as set forth in claim 12 in which said gating means includes a first and second transistor, each of which is controlled by said integrated and reference signals to provide a gating signal output during a different half cycle to an associated one of said first and second switch means.
 14. In a regulator device, a magnetic core having first and second magnetic core paths including first and second side vertical legs, a center vertical leg, and an upper and lower transverse leg, a primary winding wound on said center leg, means for connecting said primary winding to an alternating current source to provide flux in said first and second magnetic core paths on said magnetic core, load winding means wound on said magnetic core for providing an output voltage to a load, means for decoupling said source from said load, a first core winding wound on the portion of said core including said first magnetic core path and a second core winding wound on the portion of said core including said second magnetic core path, capacitor means coupled across said first and second core windings, a pair of switches, each of which is connected across a different one of said first and second core windings, the one switch for the first core winding being operative as enabled to selectively couple said capacitor means across the second core winding to drive the second magnetic core path into hard magnetic saturation and to clamp the flux in the first magnetic core path at a value which is determined by and varies with the time in a half cycle of the output voltage at which said one switch is enabled, and the other switch of said pair being operative as enabled to selectively couple said capacitor means across the first core winding to drive the first magnetic core path into hard magnetic saturation and to clamp the flux in the second magnetic path at a value which is determined by and varies with the time in an alternate half cycle of the output voltage at which the other switch is enabled, and control means for gating a different one of said switches into conduction at a selected time interval in alternate half cycles of the load voltage waveforms.
 15. A regulator device as set forth in claim 14 in which said load winding means comprises one load winding wound on said center vertical leg.
 16. A regulator device as set forth in claim 14 in which said load winding means comprises a first winding wound on the first of said sidE vertical legs and a second load winding wound on the second of said side vertical legs.
 17. A regulator device as set forth in claim 14 which includes a capacitor winding wound on said center leg, and in which said capacitor means are connected to the output of said capacitor winding.
 18. A regulator device as set forth in claim 14 in which each switch of said pair is operative as enabled to clamp the flux level in a corresponding one of aid paths, and which includes adjustable means for providing a reference signal to said control means indicating the value at which regulation is to be provided, and in which said control means adjusts the time of conduction by said switches to change the flux level in the first and second parallel magnetic core paths at which clamping occurs to thereby achieve the desired regulation.
 19. In a regulator device, a transformer structure having a magnetic core which has a center leg over which first and second magnetic paths are established, primary winding means wound on said center leg of the magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means including load winding means wound on said center leg of said core for providing an output voltage proportional to the rate of change of flux in said first and second paths, a first core winding wound on said center leg for said first magnetic path and a second core winding wound on said center leg for said second magnetic path, magnetic shunt means for decoupling said source from said secondary windings, capacitor means coupled across said first and second core windings, switching means including a first switch means coupled across said first core winding to control current conduction from said capacitor over the second core path to drive said second magnetic core path into hard magnetic saturation and to clamp the flux in said first magnetic core path at a selected level which varies with and is determined by the time in a first half cycle of the output voltage at which said first switch means is enabled, and a second switch means coupled across said second winding to control current conduction from said capacitor over said first core path and to clamp the flux level in said second core path at a selected level which is determined by and varies with the time in a second half cycle of the output voltage at which said second switch means is enabled, and control means for selectively enabling said first and second switch means in alternate half cycles.
 20. A regulator device as set forth in claim 19 in which said load winding means includes a first and a second load winding and in which said means for decoupling said source from said secondary windings comprising a first and second magnetic shunt member located on said center leg, and in which said primary winding is wound on said center leg between said first and second shunt members, and a first one of said load windings and a first one of said core windings are located on said center leg between the first magnetic shunt and one end of said center leg and the second one of said load windings and the second one of said core windings are located on said center leg between the second magnetic shunt and the other end of said center leg.
 21. In a regulator device, a first transformer having a first magnetic core which has a first magnetic path, a first primary winding wound on said first magnetic core including means for connecting said primary winding to an alternating current source, secondary winding means wound on said first magnetic core including first load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said first magnetic path, and a first core winding for said first magnetic path, and means for decoupling said first primary winding from said secondary winding means; a second transformer having a second magnetic core which has a second magnetic path, a second primary winding wound on said second magnEtic core including means for connecting said second primary winding to said alternating current source in parallel with said first primary winding, secondary winding means wound on said second core including second load winding means for providing an output voltage to a load which is proportional to the rate of change of flux in said second magnetic path, and a second core winding for said second magnetic path, magnetic shunt means for decoupling said source from said further secondary winding means, capacitor means coupled across said first and second core windings, and switching means including a first switch means as enabled in only a first half cycle of the load voltage to selectively couple said capacitor means across the second one of said core windings to drive said second magnetic path into hard magnetic saturation by said capacitor means and to clamp the flux level in the first one of said magnetic paths at a selected value which varies with and is determined by the time in the first half cycle at which said first switch means is enabled, and a second switch means coupled across said second winding operative as enabled in a second half cycle of the load voltage to selectively connect said capacitor means across the first core winding to drive said first magnetic path into hard magnetic saturation and to clamp the flux level in the second one of said magnetic paths at a value which varies with and is determined by the time in the second half cycle at which said second switch is enabled, and control means for selectively gating a different one of said first and second switch means in each half cycle.
 22. A regulator device as set forth in claim 21 in which each of said transformers include a center leg, and the primary and secondary windings for each transformer are wound on its center leg. 